This invention pertains generally to enhancing the assessment of a subject's hemodynamic condition via a newly proposed, non-invasive, three-dimensional, vector method for monitoring this condition. More particularly, it relates to a vector method, and to an associated, computer-based systemic setting appropriately provided for implementing this method, for monitoring a subject's hemodynamic condition utilizing sound-based information detected exclusively by an externally anatomically-attached, stably positioned, three-orthogonal-axis accelerometer in steps, broadly stated, which feature (a) attaching a three-orthogonal-axis accelerometer in a stable position externally to a subject's anatomy, (b) during at least one cardiac cycle of the subject, collecting signal data from the so attached accelerometer, (c) processing such collected data to obtain associated vector magnitude and directionality information, and (d) analyzing such vector magnitude and directionality information for assessment of the sought, subject's hemodynamic condition. As is pointed out below, where enhanced data-collection accuracy is desired, particularly in relation to the matter of heart murmur, plural, three-orthogonal-axis accelerometers are employed, placed in appropriate, spaced, stable, positions externally to a subject's anatomy.
The steps of this method will normally be practiced, aided by a suitably programmed, alliance, digital computer, by (or under the direct control of) a skilled medical clinician, beginning with the “attaching” step, and concluding with the combined “analyzing” and “assessing” step—this latter, combined step being performable in conjunction with the analytical knowledge possessed by such a clinician, aided in whole or in part by such a computer. Much of the process of such analyzing and assessing, beyond the important provision (by practice of the invention) of time-marked, vector-established, frequency-filtered magnitude and directionality information derived ultimately from the employed three-axis accelerometer structure, will be handled conventionally by the clinician/computer “alliance”.
In one, important form of the invention, beyond that form which features the use of just a single accelerometer, plural, similar, and similarly attached, accelerometers are employed. This mode is especially useful in relation to capturing the most robust murmur information.
In all instances, given the state of the art today involving the making of extremely tiny mechanical and electromechanical structures, a three-orthogonal-axis accelerometer, hereinafter referred to frequently simply as a three-axis accelerometer, usable in the practice of the present invention might typically have dimensions on the order of about 5×5×2-mms. Such a device might be “stand-alone” in nature, or it might be structured in combination with relevant, appropriate, algorithmically programmed, signal-data-processing and recording micro-circuitry, either “structural approach”, of course, coming with appropriate, readily externally accessible, signal-output connection structure(s). It will be immediately apparent to those skilled in the art that such an accelerometer, as well as all, appropriate signal-data-processing circuitry, including digital computer data-processing and recording circuitry, and algorithmic methodology (as such are described functionally and organizationally below both in high-level text and in block/schematic drawing form) needed to implement the data-handling and result-assessing aspects of the invention, may be conventional in nature, and may take on a number of different, entirely adequate forms. The details of these matters do not form any part of the present invention, and they are, accordingly, not discussed or elaborated herein in great detail. Rather, they are mentioned in the practice of the invention, as just suggested, in appropriate, high-level disclosure terms.
Useful background information regarding such data-processing and algorithmic circuitry and methodology employing digital computer structure, may be found in the following documents, the entire contents of which are hereby incorporated herein by reference: U.S. Pat. No. 7,096,060 to Arand et al., issued Aug. 22, 2006, for “Method and System for Detection of Heart Sounds”; and U.S. Patent Application Publication No. 2007/0191725 of Nelson, published Aug. 16, 2007, for “Wavelet Transform and Pattern Recognition Method for Heart Sound Analysis”. Signal-processing algorithmic methodology described in these documents may be employed very satisfactorily in the signal-processing environment associated with practice of the present invention. This point is reiterated later herein in a discussion specifically describing acquired-signal data processing.
Continuing, the method of the invention recognizes that three-dimensional vector sound-based (heart sound and murmur) information, which is contained collectively in all three of the traditional, three, orthogonal axes of anatomical information that may be obtained from a stably positioned, externally anatomically-attached, three-axis accelerometer, is definitively more than that which is traditionally obtained/obtainable from a single-axis (very common), or even a dual-axis (not very common) approach, and that this caliber of information offers a new and powerful route toward developing a convincing, enhancedly-detailed and reliable, assessment of a person's hemodynamic condition. In this regard, the present invention leads an important departure from the years-long lesser approaches that are principally reliant on only single-axis information.
In the field of this invention, and describing a certain, well-known background context, mechanical (heart-valve) events and abnormal fluid dynamics during the cardiac cycle generate specific sounds—heart sounds and murmur (referred to herein as sound-based information, or phenomena)—which can be auscultated and/or detected through mechanical sensors systems placed in contact with the human chest. The temporal and frequency aspects of those phenomena is very specific (a) to each of the different heart sound types (S1, S2, S3, and S4), also referred to herein as heart sounds, and as heart sound components (certain ones of which components includes each a pair of ventricle-specific, left-side and right-side sub-components), and (b) to murmur.
Regarding murmur, or murmurs, conceptually, murmurs are classified as (1) “inflow tract” murmurs of the left side of the heart; (2) “outflow tract” murmurs of the left side of the heart; (3) “inflow tract” murmurs of the right side of the heart; (4) “outflow tract” murmurs of the right side of the heart; and (5) murmurs produced at the site of any left-to-right shunt. In terms of the practice of the present invention, while, according to the preferred form of the invention, very useful vector information regarding such murmurs, or simply, collectively “murmur”, can be obtained using a single, three-axis accelerometer stably positioned on the chest, it will in some instances be more useful to employ two or more accelerometers suitably stably anchored to the chest at appropriately spaced locations to pin-point this phenomenon.
Murmur information, as compared with heart sound information, may be collected, to some extent effectively, by a single, three-axis accelerometer placed at one of the precordial, ECG anatomical sites known as V3 and V4, and preferably at the V4 site. but it is much more effectively, and clearly identifiably, collected by plural such accelerometers place at several (below identified) sites which are among the recognized traditional auscultation sites. The present invention proposes different practice modes and system arrangements which differentially recognize these two situations.
The predominantly low frequency characteristic of heart sounds (particularly), and to some extent of murmur, leads to the fact that the wave propagation from their originating sites in the heart to the chest, particularly in the cases of the several, recognized heart sounds, is not solely longitudinal, but more transversal of nature, with propagation speeds in the 1-10-meters-per-second range. One could describe them as being like “ocean waves reaching the shore”, in the sense that not every part of the sound wave fronts will reach the surface (the chest) at the same time. As a result, there is a measurable magnitude and phase difference, even between two locations in very close proximity to each other on the chest, which can be registered through mechanical sensor systems. Furthermore, it means that at a single chest location, classic heart sound detection systems, i.e. stethoscopes, microphones or single-axis accelerometers, will pick up only the sound energy component that is perpendicular (i.e., the z-axis, normal vector component) to the chest surface.
However, by using a stably positioned, three-orthogonal-axis accelerometer as proposed here by the present invention, a heart sound and murmur sensor system can also measure accurately the existing, sound-based, heart sound and murmur components occurring within the chest plane (i.e., along the x-axis and the y-axis). Especially, using such a three-axis accelerometer, a resolved, spatial vector, derived from acquired, three-dimensional sound components that are associated with the traveling wave of a particular sound-phenomenon, can be constructed and associated with appropriately band-pass-filtered frequency information, whereby:                (a) the magnitude (amplitude) of such a vector will provide information regarding the associated heart-source-based wave energy level, and        (b) the filtered signal frequency information, coupled with (c) the determined angle of the derived spatial vector, obtained from a spatial resolution of the individual vector components lying along the orthogonal x, y, and z axes adjacent the stable site of the accelerometer which will furnish information regarding the wave travel direction, will collectively provide accurate data regarding the specific internal heart-valve source of the detected sound-phenomenon (heart sound component, heart sound subcomponent(s), and/or murmur).        
To emphasize a significant point, such angular and filtered-frequency information, coming, as it will, ultimately from one or more positionally stabilized, external accelerometer(s), will lead toward a confident identification of the specific internal source (heart valve) of origin of the vector-detected wave. This confident source identification, enhanced, of course, where two or more positionally stabilized external accelerometers are contributors to final data, coupled with both (1) energy-level and (2) “within-the-cardiac-cycle” time-positioning data, is a decided advantage over the prior art offered by the present invention in relation to assisting in the professional, clinical assessment of a subject's hemodynamic condition.
Additionally the temporal variation of three-axis, vector magnitude and/or direction can be used to enhance the detection and classification of heart sounds in computerized systems, as well as the diagnostic and prognostic utility (hemodynamic-condition assessment) in the management of cardiovascular disease states.
Further discussing the relevant field of the present invention, classic auscultation of heart sounds and murmurs are performed with a stethoscope applied to the patient's chest wall. The sounds audible through such stethoscopes are generated by specific temporal conditions of the heart valves, and by temporal aspects of the fluid dynamics during the filling of the ventricles in the cardiac cycle. There are three principle types of sounds, or sound components, generated and detectable through a stethoscope: (1) closure sounds (S1-left-ventricle and S2-right-ventricle—each of these having two subcomponents, i.e. subcomponents originating, respectively, from the left side and the right side of the heart); (2) murmurs during the pumping (systole) and/or filling (diastole) cycle in the presence of deteriorating or defective heart valves; and (3) diastolic heart sounds (S3, S4) under abnormal filling conditions. The S1-left-ventricle sound subcomponents come, respectively, from the Mitral and Aortic valves, and the S2-right-ventricle subcomponents come, respectively, from the Tricuspid and Pulmonary valves. Each of these sound phenomena occurs in a different part of the cardiac cycle with, inter alia, a different time-frequency fingerprint. The phrase “time-frequency” used herein refers to the phenomenon that the frequency, or frequency “fingerprint”, of a particular heart-produced sound may change and have different values at different times.
In relation to conventional auscultation, there is a well known form of this practice featuring a pattern of plural, data-collection (sound-listening), auscultation sites. A typical “plurality” pattern might include either four (“classic”), or seven (“expanded”), recognized, auscultation locations as follows:
Classic                1. Aortic region. The region between the 2nd and 3rd intercostal spaces at the right sternal border (RUSB—right upper sternal border).        2. Pulmonic region. The region between the 2nd and 3rd intercostal spaces at the left sternal border) (LUSB—left upper sternal border).        3. Tricuspid region. The region between the 3rd, 4th, 5th, and 6th intercostal spaces at the left sternal border) (LLSB—left lower sternal border).        4. Mitral region. The region near the apex of the heart between the 5th and 6th intercostal spaces in the mid-clavicular line) (apex of the heart).        
Expanded*                1. Left Ventricular Area. The area centering on the apex beat, and extending to the fourth and fifth left interspaces, 2-cm. medial to the apex and laterally to the anterior axillary line. In isolated left ventricular enlargement, this area would extend medially, whilst in right ventricular enlargement it would extend laterally.        2. Right Ventricular Area. The area formed by the lower half of the sternum and the fourth and fifth left and right interspaces extending to about 2-cm. from the sternal edge. In conditions with right ventricular enlargement, this area may extend laterally, reaching the point of maximal impulse (clinical apex beat).        3. Left Atrial Area. The area located at the level of the angle of the scapula to the left of the vertebral margin and extending to the posterior axillary line.        4. Right Atrial Area. The area located at the fourth and fifth right interspaces at the right of the sternum, extending for a varying distance, at times to the right mid-clavicular line. In patients with extreme enlargement, it may extend further to the right.        5. Aortic Area. The area formed by the third, left interspace near the sternal edge, and extending across the manubrium to the first, second and third right interspaces near the sternal margin. It may include the right sternoclavicular joint, and often the suprasternal notch.        6. Pulmonary Area. The area formed by the second, left interspace near the sternal edge, extending upwards to the first, left interspace below the clavicle, and to the left sternoclavicular joint, and downwards to the third, left interspace near the sternal margin. This area may also extend posteriorly at the level of the fourth and fifth dorsal vertebrae about 2- to about 3-cm. on either side.        7. Area for Descending Thoracic Aorta. The area located over the dorsal spine (from the second to the tenth dorsal vertebrae) extending about 2- to about 3-cm. to the left of the spine.        *(Reference: P. M. Shah, S. J. Slodki, A. A. Luisada, “A revision of the “classic” areas of auscultation of the heart: A physiologic approach”, Volume 36, Issue 2, Pages 293-300, February 1964).        
Due to the relative low-frequency nature of the subject heart-produced sounds, their propagation mechanism inside the chest is not solely longitudinal, but rather, and/or also, transversal. While the related, complex, heart-produced “sound waves” are described as “sound”, the relevant signal content, which resides in a very low-frequency range, are often registered each as being more a vibration than a sound. The well known heart sounds lie in the range of about 5-Hz to about 125-Hz. Murmur sounds lie in the range of about 75-Hz to about 1.5-kHz.
Therefore, three-axis accelerometers, which are not constrained to the audible range of frequencies, are very suitable for information-acquisition purposes. A stethoscope, mechanical or electronic, picks up the nominal, single-axis component of this complex impulse wave on the chest wall only, and thus develops only limited information. Of course, this quite limited, stethoscopic-information-gathering approach is essentially what has defined external information-acquisition-for-assessment practice for decades. The present invention changes this in a particularly potent and useful way.
More especially, (a) using a stably, externally anatomically anchored, three-orthogonal-axis accelerometer, (b) constructing a spatial vector out of the three-axis information components that are acquired thereby, (c) then calculating the magnitude and phase relationship of this vector to its components, and additionally (d) using the time-frequency fingerprint of such a vector, one can achieve the following important results:                1. Significant improvement in the detection of heart sounds and murmurs;        2. Clear identification of each heart sound and of murmur with a high degree of specificity as to site of origin;        3. Clear identification of each heart sound subcomponent; and        4. As a consequence of these above, three things, a significant advance in supporting the making of a reliable and detailed assessment of a person's (a subject's) hemodynamic condition.        
In this setting, the invention may be described, broadly, as a vector method and associated systemic structure for monitoring a subject's hemodynamic condition including (1) attaching a three-orthogonal-axis accelerometer in a stable position externally to a subject's anatomy, (2) during at least one cardiac cycle of the subject, collecting signal data from the so attached accelerometer, (3) processing such collected data to obtain associated vector magnitude and directionality information, and (4) analyzing such vector magnitude and directionality information for assessment of the subject's hemodynamic condition.
A modification of this method takes the form of employing, instead of just one, a pattern of plural, anatomy-attached, three-axis accelerometers to perform the collecting step.
Additionally, the method of the invention contemplates, a bit more specifically, that the analyzing step will include using obtained signal vector information to identify the presences of at least one of (a) a specific heart sound component and its subcomponent, and (b) murmur.
Yet a further way of expressing a mode of practicing the invention is that it may involve using obtained vector information to identify the presences of at least one of (a) a specific heart sound component and its subcomponents, and (b) murmur.
The proposed method also involves, as a further implementation, performing the collecting, processing and analyzing steps over a selected time interval involving plural cardiac cycles to obtain temporal information regarding the subject's heart hemodynamic condition. This temporal information may include very useful indications respecting a subject's hemodynamic condition as indicated by changes over time in signal magnitudes and vector directions.
Regarding each and all of the above ways of describing the methodologic features of the invention, an additional consideration which characterizes yet another linked and modified manner for its practice is one wherein the mentioned processing includes, additionally, obtaining signal time-frequency information and relating this to specific signal vector, magnitude and directionality information.
These and other features and advantages of the present invention will become more fully apparent as the detailed description of it which now follows is read in conjunction with the accompanying drawings.
As is true with regard content of FIG. 1, FIGS. 2 and 3 are readable, as will be explained below, to describe a methodologic implementation of each of the two illustrative practice approaches represented in FIG. 1.